The Atom and the Periodic Table
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The Atom and the Periodic Table.
Introduction: The atom is the smallest part of an element , which still has the properties of that element . The atom is a unit of matter which has a dense nucleus in the centre . This nucleus is surrounded by electrons which are negatively charged . These electrons appear in outer shells around the nucleus and the first shell is able to hold two electrons and any shell after that is able to hold up to eight electrons . At the centre of an atom in the dense nucleus you will find protons and neutrons . Protons are positively charged and neutrons are negatively charged . Protons and neutrons have a mass of one atomic mass unit as oppose to an electron where the mass is so small its value has to be taken as 0 . In most atoms there are the same number of protons as there are neutrons however this is not always true and the way in which we can go about deciphering and atom is with the use of its mass number and atomic number . The atomic number of an atom is the number of protons in that element , this is also always going to be the number of electrons in that element and there will always be the same number of electrons as there are protons . The mass number on the other hand is the number of protons and neutrons combined in an atom of that element . The word atom comes from a Greek word meaning “cannot be split”. As we know this is not the case but back in the 1800s scientists believed an atom was the smallest particle in an element . From the reading of my introduction on the atom I hope your knowledge of the atom has increased and you look forward to the rest of my project.
John Dalton:
John Dalton was born in England in 1766 . Dalton was born into a Quaker family and suffered from colour blindness . The scientist is most famous for his atomic theory . This theory has five main points which are listed below :
Elements are made of extremely small particles called atoms .
Atoms of a given element are identical in size , mass and other properties . Atoms of different elements differ in these categories .
Atoms cannot be subdivided , created or destroyed .
Atoms of different elements combine in simple , whole number ratios to form chemical compounds .
In chemical reactions , atoms are combined , separated or rearranged.
Ernest Rutherford:
Ernest Rutherford received a Nobel Prize in chemistry in 1908 for his work on radioactivity. In 1910 he and his search team performed a very important experiment which leads to the discovery of the nucleus. The experiment carried out by Rutherford and his research team to investigate how alpha particles were scattered by a piece of gold leaf/foil. The expected result of the experiment was that most of the alpha particles should pass straight through the thin foil. Some alpha particles should suffer slight deflections. Rutherford was very surprised by the results of his experiment. The large deflections can be explained if the mass and positive charges of the atom are concentrated in a small core called the nucleus.
James Chadwick: James Chadwick received a Nobel Prize in physics in 1935 for discovering the neutron. Chadwicks experiment saw alpha particles knock neutrons out of the nuclei of beryllium atoms thus discovering the neutron in the process.
J.J. Thompson:
J.J. Thompson is credited with the discovery of the electron. He received a Nobel Prize for his efforts in 1906 in physics for his work on the electron. J.J. Thompson expanded on William Crookes investigation into what happens when electricity is passed through gases. Thompsons experiment which showed that the